Excepting spoken or informal language, espèce is supposed to be used with the feminine gender. On the other hand, reading the corresponding article on Wikipedia, we should remember that the entire expression's orthography differs according to the sense being given to it (biological or not):

In normal French, one writes “Le bonobo est une espèce de singe” (some sort of monkey / kinda a monkey) but a biologist would prefer to write “Le bonobo est une espèce de primates” (a species of primates).